Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Group 12 element wikipedia , lookup
Alkaline earth metal wikipedia , lookup
Boron group wikipedia , lookup
Livermorium wikipedia , lookup
Group 3 element wikipedia , lookup
Period 3 element wikipedia , lookup
Dmitri Mendeleev wikipedia , lookup
Period 5 element wikipedia , lookup
MENDELEEV AND THE ATOMIC TABLE Dmitri Ivanovich Mendeleev, 1834 – 1907, was a Russian chemist and inventor. He is credited as being the creator of the first version of the periodic table of elements. Using the table, he predicted properties of elements yet to be discovered. In the previous session we talked about our growing understanding of the atom. Our growing realisation that the world is made up of more and different elements than Aristotle’s four essences: Earth, Water, Air and Fire. Already in 1863 there were 56 known elements, with a new one being discovered at a rate of approximately one per year. After becoming a teacher, Mendeleev wrote the definitive textbook of his time: Principles of Chemistry (two volumes, 1868–1870), in Dmitri Mendeleev in 1897 which he attempted to classify the elements according to their chemical properties. In compiling the list he noticed patterns that led him to postulate his famous periodic table. On 6 March 1869, Mendeleev made a formal presentation to the Russian Chemical Society, entitled ?The Dependence between the Properties of the Atomic Weights of the Elements”. It listed elements according to both atomic weight and valence (from Latin valentia = "strength, capacity," the chemical meaning refers to the "combining power of an element”). The presentation stated that 1. The elements, if arranged according to their atomic weight, exhibit an apparent periodicity of properties. 2. Elements which are similar in regards to their chemical properties have atomic weights which are either of nearly the same value or increase regularly. 3. The arrangement of the elements in groups of elements in the order of their atomic weights corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties. 4. The elements which are the most widely diffused have small atomic weights. 5. The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body. 6. We must expect the discovery of many yet unknown elements–for example, two elements, analogous to aluminium and silicon, whose atomic weights would be between 65 and 75. 7. The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. 8. Certain characteristic properties of elements can be foretold from their atomic weights. Mendeleev published his periodic table of all the then known elements, and predicted several new elements to complete the table. For his predicted eight new elements, he used the prefixes of eka, dvi, and tri (Sanskrit one, two, three) in their naming. He was puzzled about where to put the known lanthanides, and also predicted the existence of another row to the table which were the actinides which were some of the heaviest in atomic mass (see below). Gaallium and Germanium were found in 1875 and 1886 respectively and fitted perfectly into the two spaces provided by Mendeleev. I have gone into this in some details, because to me it shows the Sculpture in honor of Mendeleev and the uncanny human capacity to understand Nature periodic table, Bratislava, Slovakia Sculpture in Saint Petersburg The modern periodic table is a tabular display of the chemical elements, organized on the basis of their atomic numbers and chemical properties. Elements are presented in increasing atomic number. The main body of the table is a 18 × 7 grid, and elements with the same number of valence electrons are kept together in groups, such as the halogens and the noble gases. Due to this, there are gaps that form four distinct rectangular areas or blocks. Using periodic trends, the table can help predict the properties of various elements and the relations between properties. As a result, it provides a useful framework for analysing chemical behaviour, and is widely used in chemistry and other sciences. Standard form of the periodic table. The colors represent different categories of elements: Red = Alkali Metals; Fawn = Earth Metals; Green - Non = Metals; Light Blue = Noble Gases; Pink = Transition Metals; Grey = Post Transition Metals; Yellow = Halogens; Brown = Metalloids; Light Grey = Unknown Properties. The Lanthanides and Actinides fit the spot above. All versions of the periodic table only include chemical elements, not mixtures, compounds, or subatomic particles, and isotopes of a given element are represented in the same cell. Isotopes are atoms that have an excess or deficiency of Neutrons in the atomic nucleus, giving them in-between atomic weights. Last time we did speak of Neutrons as the ?packing material” between the protons of an atom. The elements are listed in order of increasing atomic number (the number of protons in the nucleus of an atom). The seven Periods rows define the number of Electrons in each Shell - 2 - 8 - 8 - 18 - 18 - 32 - 32. A new row (period) is started when the next electron shell has its first electron. Groups (Columns) are determined by the electron configuration of the atom; elements with the same number of electrons in the valence shell fall into the same columns (e.g. oxygen and selenium are in the same column because they both have 4 electrons in the outermost shell. In general, elements with similar chemical properties fall into the same group in the periodic table, Thus it is relatively easy to predict the chemical properties of an element if one knows its position in the table and the properties of the elements around it. Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements within the same group generally have the same electron configurations in their valence shell, which is the most important factor in accounting for their similar properties. It has become the most important method of classifying elements. By definition, each chemical element has a unique atomic number representing the number of protons in its nucleus, but most elements have differing numbers of neutrons among different atoms; as mentioned above, these are referred to as Isotopes. For example, while all atoms of carbon have six protons and usually six neutrons, about 1% have seven neutrons, and a very small amount have eight neutrons; so carbon has three different naturally occurring isotopes, Carbon 12 - 13 - 14. Many isotopes are unstable with varying degrees of half-life. We have talked earlier about the process of Carbon Dating, where the ratio of Carbon 12 to 13 and 14 in a test sample can give a fairly accurate date when the sample was deposited. Isotopes are never separated in the periodic table; they are always grouped together under a single element. The significance of atomic numbers to the organization of the periodic table was not appreciated until the existence and properties of protons and neutrons became understood. Mendeleev's periodic tables instead used atomic weights, which at that time worked to a fair precision. The lanthanide elements are the group of elements with atomic number increasing from 57 (lanthanum) to 71 (lutetium). They are termed lanthanide because the lighter elements in the series are chemically similar to lanthanum. In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table. This convention is entirely a matter of aesthetics and formatting practicality; The table would unwieldily wide otherwise. The name "rare earths" is sometimes used to describe all the lanthanides. This name arises from the minerals from which they were first isolated, which were uncommon oxide-type minerals. The name comes from the Greek lanthanein "to lie hidden". I was later identified as the first in an entire series of chemically similar elements and gave name to the whole series. The actinide series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The series derives its name from the group 3 element actinium. In comparison with the lanthanides the actinides show much more variable valence. All actinides are radioactive and release energy upon radioactive decay; uranium and thorium are the most abundant actinides on Earth. AK